Five California governors came together Thursday in rare bipartisan opposition to a ballot initiative they fear would harm public safety by easing punishment for drug offenders.

Proposition 5 would divert tens of thousands of drug offenders annually from prisons or jails into treatment programs. It expands on a similar initiative approved by voters in 2000.

Gov. Arnold Schwarzenegger was joined by predecessors Gray Davis, Pete Wilson, Jerry Brown, and George Deukmejian at Thursday's event at a Los Angeles County's criminal courts building in downtown.

"We've cracked down on sex offenders and drug dealers and gangs," Schwarzenegger said. "Proposition 5 will take us in the opposite direction ... It was written by people who care more about the rights of criminals."

The Yes on 5 campaign said the governors' united front shows California prisons are a bipartisan failure. Under the governors' collective watch, prison crowding ballooned to the point that federal judges are considering population limits despite the state's construction of 21 new prisons since the 1990s.

Proposition 5 shortens parole for most drug and property crimes. It prohibits sending many paroled drug offenders back to prison unless they commit a new felony or have a record of committing violent or serious crimes.

All five governors last successfully opposed a 2004 initiative that would have eased California's three-strikes sentencing law. But Deukmejian missed that event four years ago, issuing a statement instead.

"It's very rarely we get together like this, Democrats and Republicans. I love this," said Schwarzenegger, a Republican. Former Democratic Gov. Jerry Brown, now the state's attorney general, said the ballot measure "destroys accountability (and) weakens the power of judges" because it limits their ability to punish offenders who don't attend treatment programs or stay off drugs.

Davis, a Democrat, and Wilson, a Republican, both criticized state spending required under the measure. The Legislative Analyst's Office projects the measure could cost the state $1 billion a year for treatment programs. But the nonpartisan analyst says that could be more than offset because an estimated 17 percent of prison inmates would be diverted to treatment programs.

"At best this is a well intentioned idea at the wrong time," Davis said. Wilson and fellow Republicans Deukmejian and Schwarzenegger said the measure would be dangerous at any time.

"The people who got us into this mess are now teaming up with the prison guards union and opposing any solutions," said Yes on 5 spokesman Tony Newman.The wealthy, influential California Correctional Peace Officers Association this month dropped an expensive effort to recall Schwarzenegger in midterm, deciding to concentrate instead on opposing ballot measures like Proposition 5.

The union has since put more than $1.8 million into derailing the measure backed by billionaire investor and liberal activist George Soros and the New York-based Drug Policy Alliance Network.

That prompted Yes on 5 television ads this week accusing guards of supporting crowded prisons because they enjoy more overtime pay. They counter No on 5 ads that feature U.S. Sen. Dianne Feinstein calling the measure "the drug dealers' bill of rights."